"If anyone can say this (phrase) 10 times quickly, they get a prize," said Stefanie Shattuck-Hufnagel, an MIT psychologist.

In their study, the researchers tried to understand whether they could induce double sound mistakes (such as "c" and "t") with different types of tongue twisters. They recorded volunteers saying a simple list of words such as "top cop" and full-sentences such as "the top cop saw a cop top."

But "pad kid poured curd pulled cod" proved to be the hardest one to get through.

The MIT psychologists, who created the twister, said participants in the study had two reactions when they attempted this combination of words. They either failed to repeat it or stopped talking altogether, Shattuck-Hufnagel said.